The invention relates to a method and apparatus for analog-to-digital conversion, and more particularly relates to a dual-slope conversion technique in which the duration of integration of an analog signal to be converted is programmable in response to the results of the digital conversion of a previous conversion operation.
In many analytical instrumentations, signal information is retrieved in analog form and must be converted to a digital form for data handling and display by a microprocessor. There are several methods and apparatus for converting an analog signal to a digital signal, with different methods having different advantages and disadvantages. The most common techniques in the art are: dual-slope integration, successive approximations, and voltage-to-frequency conversion.
The dual-slope technique which is basically a ratiometric measurement, has good accuracy, stability and ability to integrate noise. However, the dual-slope technique is relatively slow and does not have sufficient dynamic range for today's technological demands.
Therefore, it is an object of the present invention to expand the dynamic range of a dual-slope method of analog-to-digital conversion without sacrificing accuracy, stability, or noise performance.
It is another object of the present invention to provide a standard, low cost, analog-to-digital converter in conjunction with a microcomputer, having a programmable dynamic range.
It is yet another object of the present invention to provide a novel analog-to-digital converter which is compatible with a microprocessor, but which does not monopolize the functioning of the microprocessor.